On-Chip pH Sensing with Gel Microbead Positioned by Optical Tweezers

Hisataka Maruyama1, Fumihito Arai2 and Toshio Fukuda1

1Department of Micro-Nano Systems Engineering, Nagoya University, Japan2Department of Bioengineering and Robotics, Tohoku University, Japan

9633584 黃紫郁Ref: μTAS2006

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Outline

• Introduction

• Gel-Tool Contained a pH Indicator

• Experimental

• Conclusions

• References

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Introduction

• Environment measurement in a microchip is important to the on-chip experiment.

• Conventionally, microsphere’s surface is modified by fluorescent reagents and indicators.

• A local pH sensing method in a microchip using a functional gel-tool was developed.

• Gel-tools are UV curing and adhere to the glass, but we can manipulate them by the optical tweezers.

• Measure pH value locally from the color of gel-tool using calibrated color information in YCrCb color.

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Gel-Tool Contained a pH Indicator• Gel-tool is made by salting-out of ENT-3400 (polyet

hyleneglycol, PEG) which is hydrophilic resin.

• Manipulate gel-tool by optical tweezers in a water because the relative refractive index of PEG (1.42) is higher than that of water (1.33).

Fig.1 Optical tweezerFig.2 Active pH sensing Fig.3 pH sensing gel-tool pattern

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Gel-Tool Contained a pH Indicator

Fig.4 A schematic of generation of pH sensing gel-tool

Gel-tool

Fig.5 Photograph of salting-out gel-tool

20 wt% KCl

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Gel-Tool Contained a pH Indicator• Fabrication of gel-tools takes a few minutes and is

shorter than that of the surface modification.

• Gel-tools can be used as a carrier of cells because the tool adheres to cells by attaching.

• Color information on gel-tools acquired by CCD camera is converted from RGB to YCrCb by eq(1).

Y = 0.299R + 0.587G + 0.114BCr = 0.5000R - 0.419G - 0.081B (1)Cb = -0.169R - 0.419G + 0.500B

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Experimental

• Applied Cr value for calculating pH value and pH value is calculated by eq.(2).

pH = - 0.17 × Cr + 7.1 (2)pH = 0.13 × Cb + 8.0 (3)

• Adhered gel-tools did not removed from glass even by 894 mm/s flow speed.

Fig.6 Relation between pH and Cr Fig.7 Relation between pH and Cb

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Experimental

Fig.8 A schematic of active pH sensing Fig.9 Change of pH value

(d) Return to start point

Fig.10 Active pH sensing

(a) Start point (b) 100 μm moved (c) 200 μm moved

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Fig.10 On-chip pH sensing using pH sensing gel-tool

Experimental

(b) Size adjustment(a) Manipulation of gel -tool

(d) Gel-tool pattern (pH 6)

(c) Fixation of gel-tool

(e) pH 7 (f) pH 9

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Conclusions

• Proposed the pH sensing gel-tool for local environ-ment sensing in a microchip.

• Demonstrate active pH sensing and arrangement of pH sensing gel-tool pattern.

• Make the on-chip measurement easy.

• Make great contributions for cell biology.

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References

[1] H. Maruyama, F. Arai, and T. Fukuda, Proc. of μTAS2006, pp. 1247-1249, 2006

[2] H. Maruyama, F. Arai, and T. Fukuda, Proc. of IEEE2007, pp. 806-811, 2007

[3] 林世傑 , 光學嵌住之技術探討

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